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<h1 class="title"><a class="reference external" href="../../../index.htm"><img align="middle" alt="Boost" class="align-middle" src="../../../boost.png" /></a> <tt class="docutils literal"><span class="pre">read_graphviz</span></tt></h1>

<!-- Copyright (c) 2005-2009 Trustees of Indiana University
Distributed under the Boost Software License, Version 1.0.
(See accompanying file LICENSE_1_0.txt or copy at
 http://www.boost.org/LICENSE_1_0.txt) -->
<pre class="literal-block">
namespace boost {

  template &lt;typename MutableGraph&gt;
  bool read_graphviz(std::istream&amp; in, MutableGraph&amp; graph,
                     dynamic_properties&amp; dp,
                     const std::string&amp; node_id = &quot;node_id&quot;);

  template &lt;typename MutableGraph&gt;
  bool read_graphviz(std::string&amp; str, MutableGraph&amp; graph,
                     dynamic_properties&amp; dp,
                     const std::string&amp; node_id = &quot;node_id&quot;);

  template &lt;typename InputIterator, typename MutableGraph&gt;
  bool read_graphviz(InputIterator begin, InputIterator end,
                     MutableGraph&amp; graph, dynamic_properties&amp; dp,
                     const std::string&amp; node_id = &quot;node_id&quot;);

}
</pre>
<p>The <tt class="docutils literal"><span class="pre">read_graphviz</span></tt> function interprets a graph described using the
<a class="reference external" href="http://graphviz.org/">GraphViz</a> DOT language and builds a BGL graph that captures that
description.  Using these functions, you can initialize a graph using
data stored as text.</p>
<p>The DOT language can specify both directed and undirected graphs, and
<tt class="docutils literal"><span class="pre">read_graphviz</span></tt> differentiates between the two. One must pass
<tt class="docutils literal"><span class="pre">read_graphviz</span></tt> an undirected graph when reading an undirected graph;
the same is true for directed graphs. Furthermore, <tt class="docutils literal"><span class="pre">read_graphviz</span></tt>
will throw an exception if it encounters parallel edges and cannot add
them to the graph.</p>
<p>To handle properties expressed in the DOT language, <tt class="docutils literal"><span class="pre">read_graphviz</span></tt>
takes a <a class="reference external" href="../../property_map/doc/dynamic_property_map.html">dynamic_properties</a> object and operates on its collection of
property maps.  The reader passes all the properties encountered to
this object, using the GraphViz string keys as the property keys.
Furthermore, <tt class="docutils literal"><span class="pre">read_graphviz</span></tt> stores node identifier names under the
vertex property map named <tt class="docutils literal"><span class="pre">node_id</span></tt>.</p>
<dl class="docutils">
<dt>Requirements:</dt>
<dd><ul class="first last simple">
<li>The type of the graph must model the <a class="reference external" href="MutableGraph.html">Mutable Graph</a> concept.</li>
<li>The type of the iterator must model the <a class="reference external" href="http://www.boost.org/sgi/stl/InputIterator.html">Input Iterator</a>
concept.</li>
<li>The property map value types must be default-constructible.</li>
</ul>
</dd>
</dl>
<div class="contents topic" id="contents">
<p class="topic-title first">Contents</p>
<ul class="simple">
<li><a class="reference internal" href="#where-defined" id="id2">Where Defined</a></li>
<li><a class="reference internal" href="#exceptions" id="id3">Exceptions</a></li>
<li><a class="reference internal" href="#example" id="id4">Example</a></li>
<li><a class="reference internal" href="#building-the-graphviz-readers" id="id5">Building the GraphViz Readers</a></li>
<li><a class="reference internal" href="#notes" id="id6">Notes</a></li>
<li><a class="reference internal" href="#see-also" id="id7">See Also</a></li>
<li><a class="reference internal" href="#future-work" id="id8">Future Work</a></li>
</ul>
</div>
<div class="section" id="where-defined">
<h1><a class="toc-backref" href="#id2">Where Defined</a></h1>
<p><tt class="docutils literal"><span class="pre">&lt;boost/graph/graphviz.hpp&gt;</span></tt></p>
</div>
<div class="section" id="exceptions">
<h1><a class="toc-backref" href="#id3">Exceptions</a></h1>
<pre class="literal-block">
struct graph_exception : public std::exception {
  virtual ~graph_exception() throw();
  virtual const char* what() const throw() = 0;
};

struct bad_parallel_edge : public graph_exception {
  std::string from;
  std::string to;

  bad_parallel_edge(const std::string&amp;, const std::string&amp;);
  virtual ~bad_parallel_edge() throw();
  const char* what() const throw();
};

struct directed_graph_error : public graph_exception {
  virtual ~directed_graph_error() throw();
  virtual const char* what() const throw();
};

struct undirected_graph_error : public graph_exception {
  virtual ~undirected_graph_error() throw();
  virtual const char* what() const throw();
};

struct bad_graphviz_syntax: public graph_exception {
  std::string errmsg;

  bad_graphviz_syntax(const std::string&amp;);
  virtual ~bad_graphviz_syntax() throw();
  virtual const char* what() const throw();
};
</pre>
<p>Under certain circumstances, <tt class="docutils literal"><span class="pre">read_graphviz</span></tt> will throw one of the
above exceptions.  The three concrete exceptions can all be caught
using the general <tt class="docutils literal"><span class="pre">graph_exception</span></tt> moniker when greater precision
is not needed.  In addition, all of the above exceptions derive from
the standard <tt class="docutils literal"><span class="pre">std::exception</span></tt> for even more generalized error
handling.</p>
<p>The <tt class="docutils literal"><span class="pre">bad_parallel_edge</span></tt> exception is thrown when an attempt to add a
parallel edge to the supplied MutableGraph fails.  The DOT language
supports parallel edges, but some BGL-compatible graph types do not.
One example of such a graph is <tt class="docutils literal"><span class="pre">boost::adjacency_list&lt;setS,vecS&gt;</span></tt>,
which allows at most one edge can between any two vertices.</p>
<p>The <tt class="docutils literal"><span class="pre">directed_graph_error</span></tt> exception occurs when an undirected graph
type is passed to <tt class="docutils literal"><span class="pre">read_graph</span></tt> but the textual representation of the
graph is directed, as indicated by the <tt class="docutils literal"><span class="pre">digraph</span></tt> keyword in the DOT
language.</p>
<p>The <tt class="docutils literal"><span class="pre">undirected_graph_error</span></tt> exception occurs when a directed graph
type is passed to <tt class="docutils literal"><span class="pre">read_graph</span></tt> but the textual representation of the
graph is undirected, as indicated by the <tt class="docutils literal"><span class="pre">graph</span></tt> keyword in the DOT
language.</p>
<p>The <tt class="docutils literal"><span class="pre">bad_graphviz_syntax</span></tt> exception occurs when the graph input is not a
valid GraphViz graph.</p>
</div>
<div class="section" id="example">
<h1><a class="toc-backref" href="#id4">Example</a></h1>
<p>The following example illustrates a relatively simple use of the
GraphViz reader to populate an <tt class="docutils literal"><span class="pre">adjacency_list</span></tt> graph</p>
<pre class="literal-block">
// Vertex properties
typedef property &lt; vertex_name_t, std::string,
          property &lt; vertex_color_t, float &gt; &gt; vertex_p;
// Edge properties
typedef property &lt; edge_weight_t, double &gt; edge_p;
// Graph properties
typedef property &lt; graph_name_t, std::string &gt; graph_p;
// adjacency_list-based type
typedef adjacency_list &lt; vecS, vecS, directedS,
  vertex_p, edge_p, graph_p &gt; graph_t;

// Construct an empty graph and prepare the dynamic_property_maps.
graph_t graph(0);
dynamic_properties dp;

property_map&lt;graph_t, vertex_name_t&gt;::type name =
  get(vertex_name, graph);
dp.property(&quot;node_id&quot;,name);

property_map&lt;graph_t, vertex_color_t&gt;::type mass =
  get(vertex_color, graph);
dp.property(&quot;mass&quot;,mass);

property_map&lt;graph_t, edge_weight_t&gt;::type weight =
  get(edge_weight, graph);
dp.property(&quot;weight&quot;,weight);

// Use ref_property_map to turn a graph property into a property map
boost::ref_property_map&lt;graph_t*,std::string&gt;
  gname(get_property(graph,graph_name));
dp.property(&quot;name&quot;,gname);

// Sample graph as an std::istream;
std::istringstream
  gvgraph(&quot;digraph { graph [name=\&quot;graphname\&quot;]  a  c e [mass = 6.66] }&quot;);

bool status = read_graphviz(gvgraph,graph,dp,&quot;node_id&quot;);
</pre>
</div>
<div class="section" id="building-the-graphviz-readers">
<h1><a class="toc-backref" href="#id5">Building the GraphViz Readers</a></h1>
<p>To use the GraphViz readers, you will need to build and link against
the &quot;boost_graph&quot; library. This library can be built by following the
<a class="reference external" href="../../../more/getting_started.html#Build_Install">Boost Jam Build Instructions</a> for the subdirectory <tt class="docutils literal"><span class="pre">libs/graph/build</span></tt>.</p>
</div>
<div class="section" id="notes">
<h1><a class="toc-backref" href="#id6">Notes</a></h1>
<blockquote>
<ul class="simple">
<li>The <tt class="docutils literal"><span class="pre">read_graphviz</span></tt> function does not use any code from the
GraphViz distribution to interpret the DOT Language.  Rather, the
implementation was based on documentation found on the GraphViz web
site, as well as experiments run using the dot application.  The
resulting interpretation may be subtly different from dot for some
corner cases that are not well specified.</li>
<li>On successful reading of a graph, every vertex and edge will have
an associated value for every respective edge and vertex property
encountered while interpreting the graph.  These values will be set
using the <tt class="docutils literal"><span class="pre">dynamic_properties</span></tt> object.  Those edges and
vertices that are not explicitly given a value for a property (and that
property has no default) will be
given the default constructed value of the value type.  <strong>Be sure
that property map value types are default constructible.</strong></li>
<li><tt class="docutils literal"><span class="pre">read_graphviz</span></tt> treats subgraphs as syntactic sugar.  It does not
reflect subgraphs as actual entities in the BGL.  Rather, they are
used to shorten some edge definitions as well as to give a subset
of all nodes or edges certain properties. For example, the
DOT graphs <tt class="docutils literal"><span class="pre">digraph</span> <span class="pre">{</span> <span class="pre">a</span> <span class="pre">-&gt;</span> <span class="pre">subgraph</span> <span class="pre">{b</span> <span class="pre">-&gt;</span> <span class="pre">c}</span> <span class="pre">-&gt;</span> <span class="pre">e</span> <span class="pre">}</span></tt> and
<tt class="docutils literal"><span class="pre">digraph</span> <span class="pre">{</span> <span class="pre">a</span> <span class="pre">-&gt;</span> <span class="pre">b</span> <span class="pre">-&gt;</span> <span class="pre">e</span> <span class="pre">;</span> <span class="pre">a</span> <span class="pre">-&gt;</span> <span class="pre">c</span> <span class="pre">-&gt;</span> <span class="pre">e</span> <span class="pre">;</span> <span class="pre">b</span> <span class="pre">-&gt;</span> <span class="pre">c}</span></tt> are equivalent.</li>
<li>Subgraph IDs refer to subgraphs defined earlier in the graph
description.  Undefined subgraphs behave as empty subgraphs
(<tt class="docutils literal"><span class="pre">{}</span></tt>).  This is the same behavior as GraphViz.</li>
</ul>
</blockquote>
</div>
<div class="section" id="see-also">
<h1><a class="toc-backref" href="#id7">See Also</a></h1>
<p><a class="reference external" href="write-graphviz.html">write_graphviz</a></p>
</div>
<div class="section" id="future-work">
<h1><a class="toc-backref" href="#id8">Future Work</a></h1>
<blockquote>
<ul class="simple">
<li>Passing port information to BGL.</li>
<li>Expanding escape codes in the same way GraphViz does.</li>
<li>Support for optional recognition of subgraphs as distinct entities.</li>
</ul>
</blockquote>
</div>
</div>
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